The present invention relates to ultrasonic systems of the pulse echo type which are particularly suited for use in medical diagnosis. Ultrasonic systems are in use today and serve as an excellent tool in obtaining graphic displays of body internal configuration. A conventional system includes a transmitter, an ultrasonic transducer, a receiver, and a display unit.
In use, the transducer is positioned at the skin, the transmitter provides an ultrasonic pulse to the transducer which in turn launches an ultrasonic pulse into the body. The echoes produced by various discontinuities in the body (such as variations in the density of internal organs) are picked up by the transducer, converted into electrical signals and sent to the receiver which in turn provides signals to the display unit.
The transducer may be moved along the surface of the body and the angle of orientation of the transducer may be changed to scan a complete section through the body, with the resultant picture having something of an appearance of an x-ray picture. Ultrasonic systems of the foregoing type are divided into two primary categories; those providing a still frame display and those providing a real time display.
Those systems providing a still or frozen display utilize a B-contact scanner which require that the operator of the unit move the probe to "accumulate" the image for viewing. The resultant image is a form of snapshot or "still picture" which the physician can later use to diagnose various patient conditions. The real type systems utilize mechanical or spatial electronic means to move the beam of sound energy across the patient's body without actual motion by the examiner. Those systems utilizing special electronic means utilize an elongated bar having a large plurality of small transducers embedded therein. By sequentially pulsing the transducers, it is possible to electronically scan an entire "slice" of the patient's body without moving the elongated bar. In those systems utilizing mechanical means, a single small probe is rapidly pivoted in an arc which causes the sonic beams transmitted by the transducer to traverse an entire "slice" of the patient's body. In this case, the viewer shows a conical image rather than a square image, with the point of the conical image extending from the pivot point of the transducer.
In each of the foregoing systems, the ultrasonic pulse generated by the transducer is reflected from the various discontinuities in the body and are returned along the propagation path to the originating transducer. The intensity of the echo is proportional to the density and size of the reflecting object and the time delay between the initial transmitted pulse and the return echo is proportional to the distance between the source of the transmitted pulse and the reflecting object.
A major difficulty which is encountered in obtaining a suitable display of the return echo information in such systems is the fact that the format of the returned echo information is different from that of the format of the television Raster type display. The echo information may be different from the television display requirements in two primary parameters; spatial and time. The spatial parameters are at odds when the echo signal is in a conical form (such as that received when using a pivoting transducer) and the television information is in the standard Raster type rectangular form. The time parameters vary due to the fact that a typical scan rate of the transducer (as high as one-fifth of a second) is substantially slower than the required scan rate for the TV display (typically 30 frames per second). Slower scan rates produce an undesirable "flicker" in the TV display.
To overcome the foregoing problems, the prior art utilizes a scan converter for receiving and storing the incoming data from the receiver while in a write mode and for providing a video signal to the TV monitor tube during the read mode. A suitable scan converter for this purpose is disclosed in U.S. Pat. No. 4,099,179 issued in the name of Steven R. Hofstein and assigned to the assignee of the present invention. The specification of the foregoing patent is incorporated herein by reference.
The primary advantage of ultrasonic scanning systems over the more common x-ray system, is the safety of the ultrasonic systems. The hazards of x-radiation are well known and need not be reviewed herein. This hazard is overcome by the use of the relatively safe ultrasonic signals generated by the ultrasonic transducer. The major drawback of the ultrasonic systems are their relative lack of clarity. While the display provided by ultrasonic systems provide a useful indication of the general shape and structure of internal organs, the definition of the visual displays provided by such systems is not extremely high. Accordingly, it is necessary for the physician utilizing the ultrasonic system to know what portion of the body he is scanning in order to properly interpret the video information provided on the television display. That is, the physician must know which organ or organs he is scanning to properly interpret the visual display. Which organ is being scanned at any given instant is a function of both the location of the transducer relative to the patient's body and the angle of propagation of the sonic signals. Thus, the physician must know both the position of the transducer and its angle relative to the patient.
For this reason, it has been necessary for specially trained physicians to utilize the ultrasonic scanning apparatus. While these individuals have become very adept at interpreting what "slice" of the body the probe is scanning, this requirement has made the ultrasonic probe impractical for general use by physicians.